The MPLS-TP is a connection-oriented packet transport technology based on Multiprotocol Label Switching (MPLS) defined by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T). An MPLS-TP data forwarding plane is a subset of the MPLS, data of the MPLS-TP data forwarding plane are forwarded based on MPLS-TP labels. The MPLS-TP is an application of the MPLS in a transport network, it simplifies certain complicated functions of the MPLS-TP data forwarding plane and increases functions such as connection-oriented Operation Administration and Maintenance (OAM) and recovery protection and so on.
Configurations of an MPLS-TP service are divided into two parts: a Virtual Private Network (VPN) part and an MPLS-TP tunnel part respectively; the VPN part is mainly used for accessing data messages of a private network user side to a public network tunnel side or accessing data messages of the public network tunnel side to the private network user side, we call a configuration close to the private network user side as a user side interface configuration, and it contains information of user access (such as an interface type and an interface content); and we call a configuration close to the public network tunnel side as a network side interface configuration, and it contains information such as a public network label list, a private network label list and a tunnel next hop.
Configurations of an MPLS-TP tunnel are on nodes, each node is a segment of the tunnel, which can be for egress and ingress, but not all the nodes have the egress and ingress; there is no ingress at the head of the tunnel (i.e. a head node), and the missing ingress is replaced with VPN access. Similarly, there is also no egress at the tail of the tunnel (i.e. a tail node), and the missing egress is also replaced with the VPN access.
When common data access a network side through a user side, they will be marked with a public network label and a private network label of the network side and forwarded to an opposite terminal device through the public network label in the network, and at the egress of the public network, that is, when the data access the user side from the network side, the public network label and private network label will be stripped, and the original data are restored and forwarded.
There are mainly two linear protection types of the MPLS-TP tunnel, which are respectively:                a protection type 1+1: a duplicator exists at the ingress of the tunnel (i.e. at the head node), a data message will be duplicated as two copies, one copy is sent to an active tunnel, the other copy is sent to a protection tunnel, and it is required to forward a valid message and discard an invalid message at the egress of the tunnel (i.e. at the tail node or tail end);        a protection type 1:1: a selector exists at the ingress of the tunnel, it will decide whether to send the data message through an active tunnel or through a standby tunnel; and it is also required to forward a valid message and discard an invalid message at the egress of the tunnel.        
How to forward and discard the messages by the tunnel tail node is a considerable problem.